Amplifier and radiation detector

ABSTRACT

In a preamplifier (amplifier) for the radiation detector, an interconnection layer connected to the bonding pad forms one electrode of a feedback capacitor. Since there is no wiring for connecting the bonding pad and capacitor, a parasitic capacitance caused by the wiring will not be generated. Moreover, the capacitor is arranged below the bonding pad with a conductive layer serving as the other electrode, so that the feedback capacitance of the capacitor is included in the parasitic capacitance between the interconnection layer and the substrate. Compared to the conventional case, an amount of capacitance corresponding to the parasitic capacitance caused by wiring and the feedback capacitance for the capacitor is reduced from the input capacitance. Thus, the input capacitance for the amplifying circuit is reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application of U.S. patent application Ser. No.14/418,633, filed Jan. 30, 2015, now U.S. Pat. No. 9,768,737, issuedSep. 19, 2017, which was a 371 national phase application of PCTInternational Application No. PCT/JP2013/070680 filed Jul. 31, 2013,which claims the benefit of Japanese Patent Application No. 2012-172331,filed Aug. 2, 2012, the entire disclosure of each of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a radiation detector, and moreparticularly, to an amplifier for converting a charge signal output froma radiation detecting element into a voltage signal and to a radiationdetector including the amplifier.

BACKGROUND INFORMATION

A radiation detector for detecting radiation such as X-rays includes aradiation detecting element like, for example, SDD (Silicon DriftDetector). The radiation detecting element outputs a charge signal inaccordance with detected radiation. The charge signal is converted intoa voltage signal by a preamplifier. Signal processing including spectrumgeneration or the like is performed based on the voltage signal.

FIG. 1 is a circuit diagram of a preamplifier in the conventionalradiation detector. A FET (Field Effect Transistor) 72 is connected at astage preceding an amplifying circuit 71. A signal from the radiationdetecting element is input to the amplifying circuit 71 through the FET72. Moreover, each of a feedback capacitor 73 and a reset switch 74 isconnected to be in parallel with the amplifying circuit 71 and FET 72.There are cases where the amplifying circuit 71 is configured with anoperational amplifier and a transistor, where the amplifying circuit 71is configured as an integrated circuit, and where the amplifying circuit71 and FET 72 are configured as one integrated circuit.

FIG. 2 is a schematic plan view illustrating a part of the structure ofa conventional preamplifier formed as a chip. FIG. 3 is a schematic viewillustrating a section of a part of the conventional preamplifier formedas a chip. A bonding pad for input is denoted by a reference number 74in the drawings. The bonding pad 74 is connected to a bonding wire 76further connected to a radiation detecting element. In the preamplifier,a metal wiring 75 is connected to the bonding pad 74 through aninterconnection layer arranged below the bonding pad 74, while thefeedback capacitor 73 is connected to the metal wiring 75. An electrode731 at the upper side of the capacitor 73 is connected to the metalwiring 75 while an electrode 732 at the lower side thereof is connectedto an output terminal of the preamplifier. The electrode 731 at theupper side of the capacitor 73 is also connected to the FET 72 throughthe metal wiring 75. The components in the preamplifier are formed on asilicon (Si) substrate 77 while a part excluding the upper surface ofthe bonding pad 74 is covered with an oxide film (not shown). Thus, theconventional preamplifier is formed as an integrated circuit. JapanesePatent Application Laid-Open No. 2000-58765 discloses an example of anintegrated circuit including a bonding pad and a capacitor.

SUMMARY

As shown in FIG. 3, the conventional preamplifier causes a parasiticcapacitance between an interconnection layer below the bonding pad 74and, for example, the substrate 77, and also between the metal wiring 75and, for example, the substrate 77. The parasitic capacitance is alsocaused in each of the radiation detecting element, bonding wire 76 andFET 72. Thus, the parasitic capacitance for each of the radiationdetecting element, bonding wire 76, bonding pad 74, metal wiring 75 andFET 72 as well as the feedback capacitance of the capacitor 73 areincluded in the input capacitance for the amplifying circuit 71. As theinput capacitance for the amplifying circuit becomes larger, noiseincluded in a signal output by the preamplifier is increased. In theradiation detector including the preamplifier, the energy resolution ismore deteriorated as the noise included in the signal is increased. Itis thus necessary to reduce the input capacitance for the amplifyingcircuit to reduce the noise in order to improve the energy resolution ofthe radiation detector.

The present invention has been contrived in view of the abovecircumstances. An object of the invention is to provide an amplifier anda radiation detector with a reduced input capacitance for an amplifyingcircuit by making improvements in the arrangement of components in anintegrated circuit.

In accordance with a first embodiment, an amplifier according to thepresent invention includes a semiconductor substrate; an amplifyingcircuit integrated on the semiconductor substrate; a feedback capacitorconnected in parallel to the amplifying circuit; a first conductivelayer directly or indirectly connected to an external bonding wire; asecond conductive layer arranged on a side more toward the semiconductorsubstrate than the first conductive layer; and an insulating layerinterposed between the first conductive layer and the second conductivelayer, wherein the feedback capacitor is so configured that theinsulating layer serves as a dielectric while the first conductive layerand the second conductive layer serve as a pair of electrodes, the firstconductive layer is connected to an input terminal of the amplifyingcircuit, and the second conductive layer is connected to an outputterminal of the amplifying circuit.

In accordance with another embodiment, the amplifier according to thepresent invention further includes a bonding pad for connection to theexternal bonding wire, wherein the first conductive layer has one partinterposed between the bonding pad and the semiconductor substrate, andis connected to the bonding pad.

In accordance with another embodiment, the amplifier according to thepresent invention is characterized in that least parts of the bondingpad, the first conductive layer and the second conductive layer areorthogonally projected to the semiconductor substrate and overlap withone another.

In accordance with another embodiment, the amplifier according to thepresent invention is characterized in that the amplifying circuitincludes a MOSFET connected to the input terminal.

In accordance with another embodiment, the amplifier according to thepresent invention is characterized in that the amplifying circuitincludes a JFET connected to the input terminal.

In accordance with another embodiment, the amplifier according to thepresent invention is characterized in that the amplifying circuitincludes a bipolar transistor connected to the input terminal.

A radiation detector according to the present invention is characterizedby comprising: a radiation detecting element for generating a chargesignal at the time of detecting radiation; and an amplifier according tothe present invention for receiving a charge signal generated by theradiation detecting element through a bonding wire and converting thereceived charge signal into a voltage signal.

According to the present invention, in the amplifier used in thepreamplifier for radiation detector, the feedback capacitor isconfigured with a first conductive layer connected to and located belowthe bonding pad for input or the first conductive layer also serving asthe bonding pad and a second conductive layer located below the firstconductive layer with the insulating layer interposed in between. Sincethere is no wiring for connecting the bonding pad and the capacitor, theparasitic capacitance due to the wiring will not occur.

According to the present invention, at least parts of the bonding pad,the first conductive layer and the second conductive layer that areorthogonally projected to the substrate overlap with one another. Thecapacitance for the portion overlapping the bonding pad of the capacitoris included in the parasitic capacitance between the first conductivelayer below the bonding pad and, for example, the substrate. The inputcapacitance for the amplifying circuit in the preamplifier is reducedcompared the conventional case by the amount corresponding to thefeedback capacitance of the capacitor included in the parasiticcapacitance between the first conductive layer and, for example, thesubstrate.

According to the present invention, the input capacitance for theamplifying circuit is reduced compared to the conventional case, whilethe noise included in the signal output from the amplifier is alsoreduced compared to the conventional case. In the radiation detectorusing the amplifier as a preamplifier, therefore, the noise included inthe output voltage signal is reduced compared to the conventional case,while the energy resolution in the radiation detection is improved. Thepresent invention can, therefore, present such beneficial effects.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a preamplifier in the conventionalradiation detector;

FIG. 2 is a schematic plan view illustrating a part of the structure ofthe conventional preamplifier formed as a chip;

FIG. 3 is a schematic view illustrating a section of a part of theconventional preamplifier formed as a chip;

FIG. 4 is a schematic circuit diagram of a radiation detector accordingto the present invention;

FIG. 5 is a schematic plan view of a preamplifier 1 formed as a chip;

FIG. 6 is a schematic plan view illustrating the configuration of a partof a preamplifier according to Embodiment 1;

FIG. 7 is a schematic section view along the line VII-VII in FIG. 6;

FIG. 8 is a schematic plan view illustrating the configuration of a partof a preamplifier according to Embodiment 2; and

FIG. 9 is a schematic section view along the line IX-IX in FIG. 8.

DETAILED DESCRIPTIONS

The present invention will now be described below in detail withreference to the drawings illustrating the embodiments thereof.

Embodiment 1

FIG. 4 is a schematic circuit diagram of a radiation detector accordingto the present invention. The radiation detector includes a radiationdetecting element 2 for detecting radiation such as X-rays. Theradiation detecting element 2 is a semiconductor detecting element suchas a SDD. The radiation detecting element 2 generates a charge signal inproportion to radiation energy upon entrance of radiation. The outputterminal of the radiation detecting element 2 is connected to apreamplifier 1. The preamplifier 1 is an amplifier of the presentinvention. The radiation detecting element 2 outputs a charge signal,while the preamplifier 1 converts the charge signal output from theradiation detecting element 2 into a voltage signal proportionate to theenergy of radiation. The output terminal of preamplifier 1 is connectedto the output terminal of the radiation detector.

The radiation detector is included in, for example, an X-ray detectionapparatus, the output terminal of the radiation detector being connectedto the signal processing unit via an amplifier in the X-ray detectionapparatus. The voltage signal output by the radiation detector isamplified by the amplifier and processed in a signal processing unit.For example, the signal processing unit counts a voltage signal for eachvalue to obtain spectra of the detected X-rays. In another example, theradiation detector is included in an X-ray fluorescence spectrometer,which detects fluorescent X-rays emitted from a sample and performs anX-ray fluorescence analysis on the sample.

The preamplifier 1 includes an amplifying circuit 11 with an inputterminal thereof connected to the radiation detecting element 2. Acharge signal from the radiation detecting element 2 is input to theamplifying circuit 11. The FET required for inputting signals to theamplifying circuit 11 is included in the amplifying circuit 11.Moreover, each of the feedback capacitor 13 and the reset switch 14 isconnected in parallel with the amplifying circuit 11. That is, each ofthe capacitor 13 and switch 14 is connected between the input terminaland the output terminal of the amplifying circuit 11. The preamplifier 1is configured as an integrated circuit formed as a chip.

FIG. 5 is a schematic plan view of the preamplifier 1 formed as a chip.A core area 41 including the amplifying circuit 11 is provided, aroundwhich a plurality of bonding pads 43 are arranged. The bonding pads 43are connected to the core area 41 and are used for supplying power,outputting a voltage signal and inputting a pulse for resetting. Any oneof the bonding pads 43 is connected to the output terminal of theamplifying circuit 11 and serves as an output terminal of thepreamplifier 1. A bonding pad 42 for input is further arranged aroundthe core area 41. The boding pad 42 for input corresponds to the bondingpad in the present invention. The radiation detecting element 2 isconnected to the bonding pad 42 through a bonding wire (not shown inFIG. 5).

FIG. 6 is a schematic plan view illustrating the configuration of a partof the preamplifier 1 according to Embodiment 1. FIG. 7 is a schematicsection view along the line VII-VII in FIG. 6. FIGS. 6 and 7 show thebonding pad 42 for input and a portion in the vicinity of the bondingpad 42. The preamplifier 1 has a configuration in which a circuit isintegrated on a substrate 61 of Si. The substrate 61 and an oxide film62 are not illustrated in FIG. 6. The bonding pad 42 is formed to beconnected to a bonding wire 3 connected to the radiation detectingelement 2. Moreover, FIG. 6 shows each of the components orthogonallyprojected to the substrate 61.

A conductive interconnection layer 51 made of aluminum (Al) is providedbelow the bonding pad 42, i.e. between the bonding pad 42 and thesubstrate 61. The interconnection layer 51 corresponds to the firstconductive layer in the present invention. A portion of theinterconnection layer 51 located between the bonding pad 42 and thesubstrate 61 has a projection area orthogonal to the substrate 61 whichis approximately equal to that of the bonding pad 42. Thus, the bondingpad 42 is substantially superposed above this portion of theinterconnection layer 51 in plan view. Though hidden by the bonding pad42 in FIG. 6, the interconnection layer 51 is located below the bondingpad 42. An insulating oxide film 62 formed of silicon dioxide isdisposed between the bonding pad 42 and the interconnection layer 51.Via holes 57 penetrating the oxide film 62 is formed between the bondingpad 42 and the interconnection layer 51, while the bonding pad 42 isconnected to the interconnection layer 51 through the via holes 57.

The interconnection layer 51 further extends in a linear form to theoutside the region below the bonding pad 42. The extendedinterconnection layer 51 is connected to the gate electrode 54 formedwith a poly-silicon (poly-Si) layer. A source electrode 55 is providedat one side of the gate electrode 54 and a drain electrode 56 isprovided at the other side. A gate oxide film 58 is formed below thegate electrode 54, i.e. between the gate electrode 54 and the substrate61. The gate oxide film 58 is in contact with the gate electrode 54 andthe substrate 61. The gate electrode 54, source electrode 55, drainelectrode 56 and gate oxide film 58 are included in a MOSFET (MetalOxide Semiconductor FET) 12 for input which is embedded in theamplifying circuit 11. In other words, the interconnection layer 51 isconnected to the gate electrode 54 to thereby be connected to the inputterminal of the amplifying circuit 11. It is noted that the amplifyingcircuit 11 may be configured to include a JFET (Junction FET) or abipolar transistor instead of MOSFET 12.

A conductive layer 52 formed with a conductive poly-Si layer is disposedbelow the interconnection layer 51, i.e. between the interconnectionlayer 51 and the substrate 61. The conductive layer 52 corresponds tothe second conductive layer in the present invention. An insulatingoxide film 59 is formed between the conductive layer 52 and thesubstrate 61. A large part of the conductive layer 52 is overlapped bythe bonding pad 42 in a plan view when projected orthogonally to thesubstrate 61. Though hidden by the bonding pad 42 in FIG. 6, theconductive layer 52 is located below the interconnection layer 51 whichis below the bonding pad 42. That is, a large part of the conductivelayer 52 is arranged directly below the bonding pad 42. Moreover, theinterconnection layer 51 and the conductive layer 52 are arranged insubstantially parallel with each other, while an insulating oxide film62 is interposed between the interconnection layer 51 and the conductivelayer 52. Furthermore, as indicated by the broken line in FIG. 7, theconductive layer 52 is connected to another interconnection layer 53,which is connected to the output terminal of the amplifier 11. Exceptfor the upper surface of the bonding pad 42, each part of thepreamplifier 1 is covered with the oxide film 62. It is noted that theconductive layer 52 may be a metal interconnection layer. Furthermore,the interconnection layer 51 and the conductive layer 52 may be arrangedto overlap with each other in at least a part thereof in plan view.

Since the insulating oxide film 62 is interposed between the conductiveinterconnection layer 51 and the conductive layer 52, a capacitor, withthe interconnection layer 51 and the conductive layer 52 serving as apair of electrodes while the oxide film 62 serves as a dielectric, isformed. The oxide film 62 between the interconnection layer 51 and theconductive layer 52 corresponds to the insulating layer in the presentinvention. The interconnection layer 51 which is one electrode isconnected to the input terminal of the amplifying circuit 11, while theconductive layer 52 which is the other electrode is connected to theoutput terminal of the amplifier 11 through the interconnection layer53, which makes this capacitor be the feedback capacitor13.

As has been described above, in the preamplifier 1, the interconnectionlayer 51 connected to the bonding pad 42 serves as one electrode of thefeedback capacitor 13. Thus, there is no wiring for connecting thebonding pad 42 and the capacitor 13, preventing the parasiticcapacitance, which is generated in the conventional preamplifier due tosuch wiring, from being generated. Accordingly, the input capacitancefor the amplifying circuit 11 is reduced compared to the conventionalpreamplifier. It is also possible to adjust the capacitance of thefeedback capacitor 13 at the time of manufacturing, by adjusting thearea in which the interconnection layer 51 and conductive layer 52overlap with each other.

Moreover, in the present embodiment, the bonding pad 42, interconnectionlayer 51 and conductive layer 52, which are projected orthogonally tothe substrate 61, overlap with one another. It is assumed here that thearea of the bonding pad 42, the area of the interconnection layer 51below the bonding pad 42, the thickness of the oxide film 62 between theinterconnection layer 51 and the substrate 61, and the permittivity ofthe oxide film 62 are equal to those in the conventional preamplifier.Here, the parasitic capacitance between the interconnection layer 51below the bonding pad 42 and, for example, the substrate 61 will be thesame as that in the conventional preamplifier. In the preamplifier 1according to the present embodiment, on the other hand, the capacitor 13is disposed below the bonding pad 42 with the interconnection layer 51serving as one electrode, allowing the feedback capacitance of thecapacitor 13 to be included in the parasitic capacitance between theinterconnection layer 51 and, for example, the substrate 61. Compared tothe conventional preamplifier including a feedback capacitance inaddition to the parasitic capacitance caused by the bonding pad, thepreamplifier 1 according to the present embodiment has a reduced inputcapacitance for the amplifying circuit 11 by the amount of the feedbackcapacitance of the capacitor 13.

As described above, the preamplifier 1 according to the presentembodiment has a reduced input capacitance for the amplifying circuit 11compared to the conventional case. Thus, the noise included in thesignal output by the preamplifier 1 is reduced compared to theconventional case. By integrating the circuit including the amplifyingcircuit 11 on the substrate 61, the preamplifier 1 is formed at low costwhile noise may sufficiently be reduced. In the radiation detectorincluding the preamplifier 1, the noise included in the output voltagesignal is reduced compared to the conventional case, improving theenergy resolution for radiation detection. Thus, the X-ray detectionapparatus provided with the radiation detector according to the presentembodiment, for example, can detect X-rays with a high resolution. Inaddition, the X-ray fluorescence spectrometer provided with theradiation detector according to the present embodiment, for example, canperform highly accurate X-ray fluorescence analysis.

Note that the preamplifier 1 may have a form in which only a part of theportion configuring the capacitor 13 in the interconnection layer 51 andthe conductive layer 52 on the projection plane orthogonally projectedto the substrate 61 is overlapped by the bonding pad 42. Among thecapacitance for the capacitor 13, the capacitance for the portionoverlapping the bonding pad 42 on the projection plane is included inthe parasitic capacitance between the interconnection layer 51 and, forexample, the substrate 61. Thus, the input capacitance for theamplifying circuit 11 is reduced compared to the conventional case bythe amount of the capacitance for the above-described portion. The inputcapacitance for the amplifying circuit 11 is reduced compared to theconventional case also in the preamplifier 1 according to theembodiment, while the noise included in the output signal is reducedcompared to the conventional case.

Embodiment 2

FIG. 8 is a schematic plan view illustrating the configuration of a partof the preamplifier 1 according to Embodiment 2. FIG. 9 is a schematicsection view along the line IX-IX in FIG. 8. FIG. 8 is a view formed byprojecting each component orthogonally to a substrate 61, while thesubstrate 61 and an oxide film 62 are not shown. In the presentembodiment, a preamplifier 1 does not include a bonding pad 42 and viaholes 57. A part of an interconnection layer 51 forms a connectionportion 511 also serving as a bonding pad. The connection portion 511has an area large enough to be connected to a bonding wire 3 connectedto a radiation detecting element 2. The upper surface of the connectionportion 511 is not covered with the oxide film 62, so that theconnection portion 511 is connected to the bonding wire 3. Theconductive layer 52 is interposed between the connection portion 511 ofthe interconnection layer 51 and the substrate 61. A large part of theconductive layer 52 overlaps the connection portion 511 in a plan viewformed by orthogonal projection to the substrate 61. Moreover, theinsulating oxide film 62 is interposed between the connection portion511 of the interconnection layer 51 and the conductive layer 52. Theother configuration parts of the preamplifier 1 are similar to those inEmbodiment 1. It is noted that the connection portion 511 and theconductive layer 52 may overlap with each other in at least a partthereof in plan view.

In the present embodiment also, a capacitor is configured with theinterconnection layer 51 and the conductive layer 52 serving as a pairof electrodes and with the oxide film 62 serving as a dielectric, thecapacitor corresponding to the feedback capacitor 13. Since there is nowiring for connecting the bonding pad and the capacitor 13, theparasitic capacitance generated at the conventional preamplifier due tothe wiring will not be generated. Accordingly, the input capacitance forthe amplifying circuit 11 is reduced compared to the case with theconventional preamplifier. In addition, as the connection portion 511 ofthe interconnection layer 51 forms one electrode of the capacitor 13,the feedback capacitance of the capacitor 13 is included in theparasitic capacitance between the interconnection layer 51 and thesubstrate 61. Compared to the conventional preamplifier having afeedback capacitance in addition to the parasitic capacitance caused bythe bonding pad, the preamplifier 1 has a reduced input capacitance forthe amplifying circuit 11 by the amount of the feedback capacitance forthe capacitor 13. As described above, also in the preamplifier 1according to the present embodiment, the input capacitance for theamplifying circuit 11 is reduced compared to the conventional case, andthus the noise included in the signal output from the preamplifier 1 isalso reduced compared to the conventional case. The radiation detectorincluding the preamplifier 1 has an improved energy resolution fordetecting radiation. An X-ray detection apparatus including theradiation detector can detect X-rays with high resolution.

It is noted that the minimum configuration of the preamplifier 1 isdescribed in Embodiments 1 and 2, while the preamplifier 1 may includecircuit devices other than the circuit devices illustrated inEmbodiments 1 and 2. Moreover, though Embodiments 1 and 2 describedexamples where a semiconductor detecting element is used as theradiation detecting element, the radiation detector of the presentinvention may use any other radiation detecting element which outputscharge signals in accordance with detected radiation.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within metesand bounds of the claims, or equivalence of such metes and boundsthereof are therefore intended to be embraced by the claims.

1. An amplifier, comprising: a semiconductor substrate; an amplifyingcircuit; a feedback capacitor connected in parallel to the amplifyingcircuit; a reset switch integrated on the semiconductor substrate andconnected in parallel to the amplifying circuit; a first conductivelayer directly or indirectly connected to an external bonding wire forsignal input; a second conductive layer arranged on a side more towardthe semiconductor substrate than the first conductive layer; and ainsulating layer interposed between the first conductive layer and thesecond conductive layer, wherein the feedback capacitor is so configuredthat the insulating layer serves as a dielectric while the firstconductive layer and the second conductive layer serve as a pair ofelectrodes, the first conductive layer is connected to an input terminalof the amplifying circuit, and the second conductive layer is connectedto an output terminal of the amplifying circuit.
 2. The amplifieraccording to claim 1, further comprising a bonding pad for connection tothe external bonding wire, wherein the first conductive layer has onepart interposed between the bonding pad and the semiconductor substrate,and is connected to the bonding pad.
 3. The amplifier according to claim2, wherein at least parts of the bonding pad, the first conductive layerand the second conductive layer orthogonally projected to thesemiconductor substrate overlap with one another.
 4. The amplifieraccording to claim 1, wherein the amplifying circuit includes a MOSFETconnected to the input terminal.
 5. The amplifier according to claim 2,wherein the amplifying circuit includes a MOSFET connected to the inputterminal.
 6. The amplifier according to claim 1, wherein the amplifyingcircuit includes a JFET connected to the input terminal.
 7. Theamplifier according to claim 2, wherein the amplifying circuit includesa JFET connected to the input terminal.
 8. The amplifier according toclaim 1, wherein the amplifying circuit includes a bipolar transistorconnected to the input terminal.
 9. The amplifier according to claim 2,wherein the amplifying circuit includes a bipolar transistor connectedto the input terminal.
 10. A radiation detector, comprising: a radiationdetecting element for generating a charge signal at the time ofdetecting radiation; and an amplifier according to claim 1 for receivinga charge signal generated by the radiation detecting element through abonding wire and converting the received charge signal into a voltagesignal.